The use of contact lenses to correct vision is common place in today's world. There are presently several traditional methods of high-volume low-cost contact lens manufacture. These methods include, but are not limited, to cast molding, spin casting, lathing, and using a technique known in the industry as “Lightstream Technology”, and any combinations thereof.
Traditional cast molding involves the use of diamond point turning technologies to produce metal tools (also referred to as inserts) that are used in the injection molding process to produce male and female plastic lens molds. Liquid monomer is then placed between the pair of male/female molds and is then cured. Subsequently, the cured lens is removed from the mold pair and undergoes post processing steps (including hydration, release, sterilization, inspection, measurement, packaging, etc.) which results in a usable product.
Typically, spin casting also involves the use of diamond point turning technologies to produce metal tools that are used in the injection molding process to produce female plastic lens molds, into which liquid monomer is dosed. The mold and monomer are then spun about a central axis while being exposed to curing radiation and the lens is formed. Similar to cast molding, the cured lens is removed from the lens mold and undergoes post processing steps (including hydration, release, sterilization, inspection, measurement, packaging, etc.) which results in a usable product. Due to the fact that the concave surface of the lens is easily accessible when created by spin casting, this surface and lens thicknesses can be measured pre-hydration if desired.
Typically, lathing involves the use of diamond point turning technologies to produce pre-hydrated lenses directly from lens blanks (also called buttons). The pre-hydrated lens then undergoes post processing steps including hydration, sterilization, inspection, measurement, packaging, etc., which results in a usable product. Due to the fact that both surfaces of the pre-hydrated lens are easily accessible when created by diamond point turning of buttons, the pre-hydrated lens can be more fully measured in its pre-hydration state if desired.
Diamond point turning can also be used to produce the lens molds directly, with these lens molds being utilized in the cast molding or spin casting descriptions above.
“Lightstream Technology” is a technology used by Ciba Vision Corporation of Duluth, Ga. (now Alcon) which involves the use of re-usable glass mold pairs instead of plastic molds. Each glass mold pair consists of a concave surface mold and a convex surface mold that are submerged in lens monomer, placed close to each other so that the gap between the two curved surfaces map to the desired pre-hydrated contact lens profile. The monomer is cured through the glass molds using ultraviolet light, the molds separated and then the lens undergoes stages including hydration, sterilization, inspection, measurement, packaging, etc., which results in a usable product.
Most contact lenses produced and sold today are in discrete parameter ranges, which include limited base curves, diameters and powers. Sphere power offerings vary by manufacturer, but are usually in the range of −20.00 D to +20.00 D, more likely −12.00 D to +8.00 D. Typically, powers within these ranges are only offered in 0.25 D steps (between the range of −6.00 D and +6.00 D powers) and 0.50 D steps outside the ±6.00 D range. Currently, most cylinder power offerings are also in discrete steps, with each manufacturer having their own ranges. The Acuvue® brand of astigmatic lenses, manufactured and sold by Johnson & Johnson Vision Care of Jacksonville, Fla., for example, currently only offers −0.75 D, −1.25 D, −1.75 D and −2.25 D of cylinder correction. The available power axes of astigmatic lenses are also limited, typically in 10° steps, ranging from 0° to 180° for low cylinder powers, and restricted by some manufacturers further to say 80°, 90°, 100°, 170°, 180° and 190° (the 180° and 190° angles may be referred to as the 0° and 10° angles respectively) offerings for high cylinder powers.
The reasons for manufacturers only offering discrete steps in contact lens parameters are many fold, but may include the cost of tool and mold manufacture, inventory costs for storing large numbers of stock keeping units (SKUs) of the tools, inventory costs of storing huge quantities of lenses, the low prevalence of patients needing higher degrees of power correction, etc. As an example, consider the number of SKUs for a fictional astigmatic product called “BrandX” which has 1 base curve offering and 1 diameter offering. A sphere power range of −6.00 D to +6.00 D in 0.25 D steps for BrandX results in 49 different SKUs. Cylinder power offerings of say −0.75 D, −1.25 D, −1.75 D and −2.25 D along just one axis quadruples the number of SKUs to 196. Axis offerings for BrandX, say at every 10° for each of the cylinder powers, multiplies the SKUs by 18 to give 3528 SKUs. Each incremental cylinder power offering at each of the 10° axes adds 882 SKUs to BrandX's portfolio. If cylinder powers were offered in 0.25 D steps from −0.25 D to −2.25 D, the total number of BrandX SKUs would be 7938. Just one additional base curve offering doubles the SKUs to 15,876, and adding just one other diameter to the mix doubles the total again to 31,752 SKUs. Offering BrandX's axes in 5° instead of 10° increments also doubles the number of SKUs to 63,504. Offering BrandX in alternate materials also drastically increases the number of SKUs.
Offerings of different lens designs, power, base curve, diameter and shape all require different tools to be made. In a cost range of $100-$500 per metal tool, cast molding for a large number of SKUs is a very expensive proposition, especially when multi-cavity technology is used wherein multiple tools of the same design are used in each mold block. Manufacturers therefore are selective as to the number of different contact lens design options they produce, which typically are chosen to align with the most commonly prevalent vision need/ordered prescriptions. This, of course, means that individuals whose prescriptions fall between or outside those ranges offered by manufacturers must purchase lenses that are less than optimal in correcting their particular vision or fit needs.
With traditional manufacturing techniques, once the mold has been established for a given prescription, each product manufactured from that mold is labeled with that given target prescription, including power, and the lenses themselves are not further measured individually. In other words, the lenses produced are labeled with the target prescription and not labeled with respect to the actual parameters of the resulting product. Measurements are not performed on each manufactured lens since to do so each lens must be removed from the mold, hydrated, restrained and separately held. Performing these stages and precisely measuring each lens is time consuming, difficult, and expensive enough so as to be prohibitive.
In reality, high volume low cost hydrogel contact lens manufacture results in variations within each lot of lenses, and between lots. The ANSI Standard Z80.20 and BS EN ISO 18369−2:2012 standard defines as acceptable a back vertex power tolerance of ±0.25 D for the sphere power range of −10.00 D to +10.00 D, a ±0.50 D tolerance for sphere powers in the ranges of −20.00 D to −10.01 D and +10.01 D to +20.00 D, and a ±1.00 D tolerance beyond −20.00 D and beyond +20.00 D. Both standards also show tolerances on cylinder power of ±0.25 D for cylinder powers up to and including −2.00 D, a ±0.37 D tolerance for cylinder powers between the range of −2.01 D to −4.00 D, and a ±0.50 D tolerance for cylinder powers beyond −4.00 D. Manufacturers typically monitor lens parameters on a sampling basis to ensure that parameters are within upper and lower specification limits. If the mean of any measured parameter drifts too far from the desired target, manufacturers can adjust a multitude of process parameters to re-center the mean. Variations in power of high volume low cost lenses may result from many sources, which when combined with metrology inaccuracies can typically result in a ±0.15 D deviation from target, but can be anywhere within the limits described above. In summary, the actual lens power of any commercially available high-volume low-cost lens is not known exactly, as only the labeled (targeted) lens power is available for reference.
More recently, a new system and method for manufacturing contact lenses has been disclosed in which an infinite number of different lens shapes and lens parameters (including lens powers) can be produced on a custom basis. U.S. Pat. No. 8,317,505, which is incorporated herein by reference in its entirety, discloses a method for growing a Lens Precursor Form on a single male optical mandrel on a voxel by voxel basis by selectively projecting actinic radiation through the optic mandrel and into a vat or bath of liquid polymer. The optical mandrel and Lens Precursor Form are then removed from the vat and inverted so that the convex surface of the optic mandrel is upright. Following a dwell period during which uncured residual liquid monomer from the bath that remains on the Lens Precursor Form flows under gravity over the Lens Precursor Form, such liquid is then cured to form the final lens. As described therein, a custom lens can be produced for any given eye.
For customized lenses manufactured as set forth in U.S. Pat. No. 8,317,505, it is possible to measure the power of each lens as it is produced (in its pre-hydrated state and converting the values through known calibration parameters to a precise wet lens measurement, or measuring the wet powers of each completed lens after hydration) rather than relying on targeted lens power. As the formed lens is held in place on the male mandrel, precise measurements of the pre-hydrated lens can quickly and easily be performed by using any known capable technique. Examples of suitable measurement techniques include but are not limited to wavefront measurements and non-contact thickness profile measurements. Wavefront measurements may be employed in a manner and via the use of equipment such as that described in U.S. Patent Publication No. 2012/0133957, which is incorporated herein by reference in its entirety. Data from wavefront metrology can easily be transferred into aberration profile data, including sphere, cylinder and axis. Alternatively, lens thickness information may be gathered by the use of, for example, non-contact opto-mechanical profilometry. There are many pieces of equipment capable of taking these measurements, one example would be a system where a Keyence non-contact probe (Keyence Corporation of America, Itasca, Ill.) is mounted on an air bearing rotation stage, with the optic mandrel being mounted on another air bearing rotation stage and the motion of both the part to be measured and the probe are synchronized and coordinated as to map the desired surface are of the part under consideration. Data from non-contact opto-mechanical profilometry can easily be transferred into aberration profile data, including sphere, cylinder and axis. Other suitable measurement techniques and devices may also be used.
The ability to manufacture and readily measure a custom lens creates new opportunities for the eye care practitioner to be able to dispense more accurate contact lenses to their patients. For this to effectively occur, however, the eye care practitioner (ECP) must be able to identify a more precise prescription for the patient.
In a typical setting, a patient's vision will be evaluated by any known means, and an initial desired lens power will be identified. A fitting or trial lens having close to the desired power will be placed on the patient's eye, and depending on how the patient sees with that given lens, the lens power may be adjusted up or down, which with traditional lenses is limited by the commercially available 0.25 diopter steps in lens sphere power and the limited available cylindrical powers as detailed above. For traditional lenses where only label (target) power is known as opposed to the actual measured lens power of the first fitted lens or any subsequently selected lens, the process is sub-optimal. Further, the subjective refraction and over-refraction exams are typically low resolution, limited to 0.25 D increments. Consider a patient with an actual spherical power need of −2.875 D. Using course 0.25 D resolution phoropters, this vision requirement will only be measured as either −2.75 D or −3.00 D to the nearest 0.25 D increment. Assume the ECP uses the −2.75 D value as the patient's perceived need, a first fitting lens labeled as −2.75 D may be selected and placed on the eye. This lens though could actually measure anywhere from −2.50 D to −3.00 D, as per the ANSI standard. If the over-refraction exam returns a value of −0.25 D, the ECP may select another fitting lens labeled −3.00 D and repeat the exam, or order −3.00 D lenses for the patient. The delivered lenses could range from −2.75 D to −3.25 D (as per the ISO standards) but yet the patient's true need was −2.875 D, yielding sub-optimal vision correction. Consider the case where the actual sphere power of the initial fitting lens labeled as a −2.75 D was really a −3.00 D lens, then based off the −0.25 D over-refraction the lens the patient really needs would be a −3.25 D indicating that the delivered lenses to the patient could be 0.375 D away from optimal correction. This situation using a coarse refraction, unknown actual fitting lens powers and course over-refraction exams leading to sub-optimal vision applies equally to the use of astigmatic fitting lenses; commercial products used as fitting or trial lenses, and intended correction of astigmatic, multifocal, higher order aberrated and diseased eyes.
As described further below, while it is preferable that the exact powers of the fitting lenses be known, and for high resolution exams to be performed in order to obtain the best results, the system and methods of the present invention will nevertheless provide a more precise prescription for a patient regardless of whether currently available stock lenses and low resolution exams are used.
Phoropters, refractometers or aberrometers, manual or automated, are frequently used in the ECP office to determine a patient's vision requirement via refraction exams or over-refraction exams. “Refraction exams” are typically conducted through the patient's bare eye (that is when vision correction is not worn) and often referred to as “bare eye exams”. “Over-refraction exams” are performed when the patient is wearing vision correction (typically contact lenses). Both phoropters and refractometers have the capability of outputting a sphere power component, a cylinder power component and an axis component.
Glass lenses of different power are typically embedded in auto-phoropters, whereas manual phoropters basically consist of a trial frame into which ECPs can manually place supplemental glass lenses of different power. In both manual and auto-phoropters, these glass lenses are placed in the line-of-sight of the patient as he/she looks through the unit towards a vision target. While looking through the unit, the ECP selects appropriate glass lenses of different power and asks the patient which one is “better or worse”. The ECP does this to refine his/her patient's prescription. Exams performed using phoropters are typically referred to as “subjective exams” since the patient gives their opinion on which lenses are “better or worse” for them.
Typically ECPs use both manual and auto-phoropters in 0.25 D power increments although some have the capability of using 0.125 D steps, and 5° axis increments. Refractometers and aberrometers typically display power data to the nearest one hundredth of a diopter, and the nearest whole integer for axis in degrees. Exams performed using refractometers and aberrometers are typically referred to as “objective exams” since the equipment just returns numerical and graphical values, with little to no patient involvement in the decision making process. One example of an auto-refractometer is the Nidek ARK-10000 Refractive Power/Corneal Analyzer (Nidek Inc. of Freemont, Calif.). The 0.01 D power resolution and 1° axis resolution of refractometers and aberrometers suggests that they would be ideal for use in the process of prescribing custom lenses, however, objective exams performed on currently available equipment do not take into account how the brain perceives and analyzes the images presented to it by the ocular system and therefore do not always provide the best prescriptive data for all patients. When fitted with lenses prescribed via the use of subjective data compared to lenses prescribed off objective data, some patients prefer the “subjective lenses” and others prefer the “objective lenses”. This being said, the sphere, cylinder and axis data from objective exams can be used alone, or in combination with data from subjective exams to provide the best possible custom lens design for the patient.
As will be described further below, data from at least two eye exams are required for the present invention, a bare eye exam and an over-refraction exam. The exams do not need to be concurrent, but it is preferable if they are since day to day variations in eye performance can affect the results. It is also preferable, but not essential, to perform the exams using the same equipment since any differences in calibration and performance between similar but different units may also affect the results. Subjective or objective exams may be used for both the refraction and over-refraction exams, or any combination thereof.
In summary, the invention described herein will work with high resolution data, low resolution data or a combination of high and low resolution data; with data from subjective exams, objective exams or a combination of both subjective and objective exams; or with a new breed of objective equipment that purports to support subjective responses. The methods highlighted will further work with any pertinent value of sphere power, cylinder power and axis information extracted from any measurement equipment and technique, including phoropters, refractometers and aberrometers. Further, the invention described herein is applicable to all types of required vision correction needs, including single vision, multifocal vision, astigmatic vision, higher order aberration correction needs as well as diseased eyes, such as Keratoconus.